Arc Flash Hazard Analysis
Arc flash is one of the most dangerous hazards in the workplace, causing hundreds of fatalities and thousands of injuries each year. Estimates show that 5-10 arc flash incidents occur every day in the US. Organizations spend millions every year in worker's compensation, medical bills, equipment repair, OSHA fines and legal fees from arc flash. The Electrical Power Research Institute estimates direct costs to an employer from a fatal electrical accident at $1.3 million, with indirect costs adding another $2 to $8 million. Implementing an arc flash safety strategy protects company assets and employees while complying with federal law.
What is an arc flash?
An arc flash is the sudden release of electrical energy through the air when an arcing fault occurs between phase-to-phase, phase-to-neutral, or phase-to-ground conductors. An arc flash gives off thermal radiation (heat) and bright, intense light. Temperatures have been recorded as high as 35,000˚F. This extreme temperature melts and vaporizes metals and can ignite clothing and cause fatal burns as far as 10 feet away.The vaporization and expansion of metals causes an arc blast, which produces immense sound and pressure waves just as powerful as a dynamite explosion. These pressure waves can rupture eardrums, collapse lungs, and propel workers across the room or cause them to fall from ladders. Molten metal droplets and fragments of surrounding equipment will be expelled at speeds up to 700 miles per hour causing blunt-force trauma, cuts and abrasions. Inhalation of vaporized materials can be toxic. In environments that contain explosive gases or combustible materials, even low-energy arcs can create violent explosions.
An arc flash can have a variety of causes, including accidental contact with electrical systems, dropped tools, build up of conductive dust, corrosion, insulation breakdown, loose connections and improper work procedures or equipment utilization. Preventing arc flash accidents requires a multifaceted prevention strategy with an arc flash hazard study as the foundation.
If you have any questions about performing an arc flash hazard analysis at your facility, contact our Engineering Account Executive, Leisa Busbea
The term “arc flash” isn’t even used once in OSHA’s Code of Federal Regulations. So what’s the big deal? The General Duty Clause and references to NEC®, NFPA 70E® and IEEE standards are the key.
OSHA’s General Duty Clause requires employers to provide a workplace free from “recognized hazards.” Russell B. Swanson, OSHA Directorate of Construction, states, “With respect to the General Duty Clause, industry consensus standards may be evidence that a hazard is “recognized” and that there is a feasible means of correcting such a hazard.” The National Electrical Code, NFPA 70E, IEEE and NESC are among OSHA recognized industry consensus standards and are directly referenced in the regulations.
The NFPA 70E: Standard for Electrical Safety in the Workplace® specifically addresses how to deal with arc flash hazards. Article 130.3 states, “A flash hazard analysis shall be done in order to protect personnel from the possibility of being injured by an arc flash. The analysis shall determine the Flash Protection Boundary and the personal protective equipment that people within the Flash Protection Boundary shall use… It shall be reviewed periodically, not to exceed five years, to account for changes in the electrical distribution system that could affect the results of the arc flash hazard analysis.” Article 130.3(c) states “Equipment shall be field marked with a label containing the available incident energy or required level of PPE.”
We often hear of organizations using the NFPA 70E Hazard Risk Category(HRC) tables 130.7(c)(9) for arc flash protection. These tables are limited to eight specific pieces of electrical equipment. If the equipment, voltage, or task is not listed in the table, an arc flash analysis is required. The tables are based on predetermined available short circuit current and clearing time. The majority of facilities will have higher or lower current and clearing times which may result in an increased or decreased thermal hazard. Higher short circuit current can result in higher temperature and a larger flash, while lower short circuit current can result in a smaller flash but lengthen the duration of the arc flash. Using the NFPA 70E tables does not constitute compliance unless your system falls within the specific short circuit current and fault clearing times specified in the Fine Print Notes.
The National Electrical Code also addresses arc flash protection. NEC Article 110.16 states “Flash Protection. Switchboards, panelboards, and motor control centers in other than dwelling occupancies, that are likely to require examination, adjustment, servicing, or maintenance while energized, shall be field marked to warn qualified persons of potential electric arc-flash hazards. The marking shall be located so as to be clearly visible to qualified persons before examination, adjustment, servicing, or maintenance of the equipment.” Fine Print Note 1, then directs you to the NFPA 70E for “determining severity of potential exposure, planning safe work practices, and selecting personal protective equipment.”
The National Electrical Safety Code even sets a deadline for utilities to perform their arc flash studies. NESC, Section 41.410.A.3 (page 246) states “Effective as of January 1, 2009, the employer shall ensure that an assessment is performed to determine potential exposure to an electric arc for employees who work on or near energized parts or equipment. If the assessment determines a potential employee exposure greater than 2 cal/cm2 exists…, the employer shall require employees to wear clothing or a clothing system that has an effective arc rating not less than the anticipated level of arc energy.”
So who’s responsible for making this happen? OSHA has a multiemployer worksite policy (CPL2-0.124) that makes it clear that both the equipment owner and contractor are responsible for contractor safety. If an organization allows a contractor on its job site, that company has approved the contractor’s safety procedures and policies. Employees as well as contracted workers cannot always be counted on to understand arc flash protection. Labeling the equipment ensures that those who work on power system equipment will be aware of the arc flash hazard involved and the required flash protective equipment.
If you have any questions about performing an arc flash hazard analysis at your facility, contact our Engineering Account Executive, Leisa Busbea
AVO Electrical Engineering Division adheres to the following process in performing an arc flash hazard analysis. This correlates with IEEE Standard 1584, Chapter 4.
- Data from the utility, including available fault current, operating voltage, and specifics regarding the utility's protective equipment at the point of service, such as manufacturer, model, time/current settings, or fuse rating
- Specifics for each protective device in the electrical system, including manufacturer, model, available time/current settings, and short-circuit interrupting rating
- Impedance, tap setting and rating of each transformer
- Conductor specifics, including lengths, sizes, and types of all overhead lines, bus ducts, and cables
1. Data Gathering
Qualified staff must gather data from all applicable electrical equipment. This required information includes:
2. Power system modeling
One line diagrams must be developed or updated to show the current configuration and modes of operation for the power system. Accurate electrical system drawings are necessary to identify power sources, voltage levels, electrical equipment and protective devices.
3. Perform a short circuit study
A short circuit study is required to determine the magnitude of current flowing throughout the power system at critical points at various time intervals after a “fault” occurs. These calculations will be used to determine the bolted fault current, which is essential for the calculation of incident energy and interrupting ratings of your equipment. Comparison of equipment ratings with calculated short circuit and operating conditions will identify underrated equipment.
4. Perform a protective device coordination study (optional)
A protective device coordination must be performed to ensure selection and arrangement of protective devices limits the effects of an overcurrent situation to the smallest area and to provide input data for the analysis. Results will be used to make recommendations for mitigation of arc flash hazards. This is an optional service, but keep in mind that arc flash mitigation cannot be performed without this study completed.
5. Perform arc flash hazard calculations
These calculations are based on available short circuit current, protective device clearing time and other applicable one line diagram information. Calculations of incident energy levels and flash protection boundaries should be done for all relevant equipment busses. Magnitude of arc hazards are determined using methods from NFPA 70E®, IEEE 1584 or NESC Tables 410‐1 and 410‐2.
6. Install arc flash labels
Generate and install ASTM compliant, environment and chemical resistant arc flash hazard warning labels. These labels must identify incident energy, limited, restricted and prohibited approach distances, minimum arc rating, flash protection boundary distance and shock hazard when exposed to energized circuits or parts.
Learn more about what makes us the leading provider of arc flash hazard analysis. Are you ready to start preparing for your arc flash? Request a proposal.
If you have any questions about performing an arc flash hazard analysis at your facility, contact our Engineering Account Executive, Leisa Busbea